1. Field of the Invention
The present invention relates to a diffusion joining in which a mounted member is pressed against a mounting member while the mounted member and the mounting member are being heated.
2. Description of the Related Art
Diffusion joining structures as described above have already been known in JP-A-7-103070, JP-A-7-189628 and JP-A-9-122924, and the official gazettes of those unexamined patent publications disclose diffusion joining structures in which a valve seat as a mounted member is diffusion joined to a cylinder head as a mounting member, which valve seat is formed of a material different from that of the cylinder head.
In the conventional diffusion joining structures as described above, however, since the external face of a portion of the mounted member which is to be joined to the mounting member has a transverse cross-sectional configuration comprising a combination of straight lines in a state prior to joining, sufficient plastic flows are not generated at the straight line portions, and therefore a sufficient joining strength cannot be obtained. This seems to be because the plastic flow is generated sufficiently at the distal portion of the mounted member which is adapted to first be brought into contact with the mounting member when the mounted member is pressed to the mounting member since the distal portion is formed acutely to thereby generate a sufficient diffusion joining layer thereat, whereas no sufficient diffusion joining layer is formed at the portion having the straight transverse cross-sectional configuration and linking up with the distal end portion since the sliding speed and volume of the plastic flow substance are clearly reduced thereat when compared with the distal end portion.